1. Field of the Invention
The present invention relates to image processing. More particularly, the present invention relates to determining replacement pixel values for defective sensing elements of a detector array.
2. Background Information
Focal plane arrays (FPAs) are detector arrays that can be used in infrared (IR) imaging systems, such as forward looking infrared (FLIR) camera systems, and are the “eyes” of an IR sensor. Third-generation (staring) FPAs comprise a plurality of sensing elements for detecting radiation arranged in a two-dimensional configuration. Second-generation (scanning) FPAs comprise a plurality of sensing elements arranged in a one-dimensional configuration. As used herein, a one-dimensional array is intended to include a quasi-one-dimensional array known to those skilled in the art, and such as described, for example, in U.S. patent application Ser. No. 09/840,920, now U.S. Pat. No. 6,901,173, entitled “Scene-based non-uniformity correction for detector arrays”, the entire contents of which are incorporated herein by reference.
FPAs can have defective sensing elements. A defective sensing element in a scanning FPA yields an entire row of defective pixels (also called a “channel” outage) in a collected image. Defective sensing elements in a staring FPA do not result in an entire defective row of pixels of an image, but nevertheless result in a loss of image information and a reduction in the aesthetic quality of imagery obtained if not corrected.
Conventional approaches are known for determining replacement pixel values associated with defective sensing elements of an FPA. Such approaches are typically known as dead-pixel replacement or dead-cell replacement. For example, U.S. Pat. No. 6,359,681, entitled “Combined Laser/FLIR Optics System”, describes an approach for dead-cell replacement wherein a list of “dead” cells (i.e., detector elements that do not properly respond) is maintained, and wherein a pixel value corresponding to each “dead” cell is replaced with an approximation value. In the approach described therein, the approximation value is derived by averaging the values of the pixels which border the pixel corresponding to the “dead” cell, and only neighboring pixels that correspond to properly functioning detector elements are used for the purpose of deriving an approximation value. In other words, the replacement pixel according to this approach is an average of pixel values corresponding to properly functioning detector elements in a 3×3 region surrounding the defective detector element (in terms of the number of pixels).
In another conventional approach for dead-cell replacement, the pixel values of cardinal cells adjacent to a given dead (i.e., defective) cell are averaged to determine a replacement pixel value for the defective cell. The cardinal cells are those immediately adjacent cells that are positioned directly above and below the defective cell and directly to the left of and to the right of the defective cell.